1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus, and more particularly, to a photoelectric conversion apparatus comprising a plurality of photoelectric conversion elements arranged in an array form and having the capability of obtaining a reference signal used to perform a signal correction.
2. Description of the Related Art
Photoelectric conversion apparatuses generally have some amount of variation from apparatus to apparatus in the output obtained when the photo sensing area, in which the photoelectric conversion elements are arranged in an array form, is illuminated by light (the output in this state is referred to as the sensitivity) and also a variation in the output obtained when the photo sensing area is illuminated by no light (the output in this state is refers to as the offset output). To fully use the abilities of photoelectric conversion apparatus, it is desirable to correct such the variations. To this end, a photoelectric conversion apparatus generally has a correction circuit and a photoelectric conversion element used to generate an output signal, on the basis of which the correction is made.
Correction circuits such as an offset correction circuit and a sensitivity correction circuit are commercially available. However, a special photoelectric conversion element is required to generate correction data which is supplied to a correction circuit. That is, photoelectric conversion apparatuses generally have an offset correction photoelectric conversion element disposed separately from the main photoelectric conversion element array. More specifically, for example a CCD sensor made of crystalline silicon is disposed outside the photo sensing area of a photoelectric conversion apparatus, and the output signal obtained when there is no light illumination is monitored by the CCD sensor. The output signal obtained in this situation is used as correction data.
A sensitivity correction photoelectric conversion element is produced by placing a filter on a CCD sensor made of for example of crystalline silicon, and is disposed outside the photo sensing area as in the case of the offset correction photoelectric conversion element. The output signal obtained when detecting light with a certain illumination intensity within the range from 0 to 100% is monitored and supplied to a common correction circuit. The data actually generated by the photo sensing area of the photoelectric conversion apparatus is corrected on the basis of the above monitored signal.
However, when such a correction photoelectric conversion element is disposed on a photoelectric conversion apparatus separately from the main photoelectric conversion element array, a complicated circuit is required to read the output signal of the correction photoelectric conversion element. This causes a reduction in production yield of photoelectric conversion apparatus, thus causing an increase in production cost.
In the case of a photoelectric conversion apparatus including a plurality of pixels which are two-dimensionally arranged, if a circuit for reading the output signal of a correction photoelectric conversion element is disposed separately on the photoelectric conversion apparatus, additional time is required to read the correction output signal. As a result, it can become impossible to correct the output signal generated by the main photoelectric conversion elements in the remaining short time. This can make it difficult to take a moving picture.